Strengthening mechanism for copper base alloys

ABSTRACT

A copper base alloy including about 0.25 percent- 11 percent tin and about 0.1 percent- 0.5 percent molybdenum disulfide. A method of producing a copper base alloy of improved antifriction characteristics, strength, modulus of elasticity, hardness and resistance to corrosion by adding about 0.1 percent0.5 percent molybdenum disulfide.

I United States Patent [111 3,607,243

[72] Inventor Edgar C. Wallace 835,052 11/1906 Becket 75/135 X Cleveland, Ohio 990,040 4/1911 Franke 75/154 X [21] AppLNo. 781,208 2,338,344 1/1944 Marino 75/153 X [22] Filed Dec.4, 1968 2,781,258 1/1957 Niedzwiedzki 75/123 [45] Patented Sept.21, 1971 2,786,128' 1/1957 Lines 75/153 X [73] Assignee W. S. Tyler Inc. 2,918,094 12/1959 Freynik 75/154 X Cleveland, Ohio 3,045,331 7/1962 Ang 75/153 X 3,240,592 3/1966 Bray 75/154X 3,279,899 10/1966 Bangert 75/154 X [54] STRENGTHENING MECHANISM FOR COPPER 3,370,944 2/ 1968 Kawasaki 75/154 X BASE ALLOYS Primary Examiner L Dewayne Rutledge 2 Drawing 5188' Assistant Examiner-Joseph E. Legru [52] US. Cl. 75/l 54, Attorney-Fay, Sharpe and Mulholland V, we, 9., [51] Int. Cl C22c9/02 [50] FleldofSearch 75/134, I H

252/12 ABSTRACT: A copper base alloy including about 0.25 percent-l 1 percent tin and about 0.1 percent-0.5 percent molyb- [56] References Cited denum disumde UNITED STATES PATENTS A method of producing a copper base alloy of improved anl,479,859 1/ 1924 Koehler 75/ 154 X tifriction characteristics, strength, modulus of elasticity, hard- 3,208,846 9/1965 Bruma 75/153 ness and resistance to corrosion by adding about 0.1 per- 774,167 llll 9 0 4 l iyerette 7 5/ 5 3 cent-0.5 percent molybdenum disulfide.

030 STRAND ANNEALING 0mm SIZE vs TEMP.

.025 m s'ro. PHOS. RONZE 6-6.5% Tm E I E .020 I f STD. PHOS. aaouz: PHOS- BRONZE 3 0% rm W s-s.5 rm I z 5 me l 2/ APPROX. AINNEALING TIME a SEQ g mo d 0.I-O.5 '/1 NI S ,6-5-l9% TII 5 0 I u A O I 5 .005 f? n VARIOUS LOTS IFEAA 0 I I050 H00 H50 I200 I250 I500 I550 I400 I450 I500 TEMPERATURE F PATENTED we I I9?! sTRANo ANNEALING eRAIN sIzE vs TEMP. .030 .025 2 5w. PHOS. BRONZE 6-6.5 TIN ,7 LI] I .020 5 sm PHOS. BRONZE o S PHOS; BRONZE 8% rm w 0 Tm I 5% TIN O i .Ol5 i I API =R0x. ANNEALIIIVG TIME 6 sEc;

(I :3 01-05% M S;,6.5-'l9% TIN 6 .OIO A1 1 5 0 0 c% u IA/IIA 4 0 [J g f .005 .A,

vARIous LOTS F] G I I: 0 AA I050 II00 "50 I200 I250 I300 I350 I400 I450 I500 TEMPERATURE F v- 80 I l I l l l I Loss IN SL RFACE HARDNESS PoR vARIous P0uR0RINIER STD. MATERIALS I BRNZE STAINLESS WOOD STEEL WOOD BRONZE HARDNESS TAKEN AFTER gg gg T WEARING TEsT IN 5 PAP|ERMILL soLuTIoNs I 850 WOOD a PLAsTIc 0) 3w SAMPLE 2 SA LE SLIII')ERS U'SED Z5 WOOD I 22 HD HM p HIGH DENSITY-HIGH E QQ BE MOLECULAR WT. PE :2 2000 W000 3 END GRAINED HARD MAPLE g ao L: 5 sAIvIPLE 2| HD I-INI PE GRADE 8 I900 35 I0 INVENTOR FIG. 2

EDGAR C. WALLACE 4A,, 5% a Mal/mflwd ATTORNEYS STRENGTHENING MECHANISM FOR COPPER BASE. ALLOYS BACKGROUND OF THE INVENTION There is always a need for alloys of any material havinga higher strength, a lower coefficient of friction, a slower grain growth rate with annealing and a higher modulus of elasticity. Obviously copper alloys are included. Because of involvement in this field and with a desire to provide a strengthened copper alloy, experiments were conducted which included adding molybdenum-coated particles of molybdenum disulfide to a copper-tin alloy. From a knowledge of the properties of such molybdenum disulfide particles, if molybdenum disulfide could be incorporated in the alloy, it could be expected that the resulting alloy would have a lower coefficient of friction and upon annealing, the growth rate of the grains of this alloy would be somewhat slowed in accordance with the wellknown principles of grain growth, i.e., impurities in or out of solution generally inhibit grain growth. However, something unexpected occurred, the resulting alloy had a lower coefficient of friction, a grain growth inhibition which was even greater than anticipated, an improved yield strength, an improved tensile strength, an improved modulus of elasticity and curved twin boundaries in some of the alloy grains. The combination of these unexpectedly improved properties has lead to several very important advances unexpectedly certain fields which had previously been stagnant for a lack of proper materials.

To be more specific, this invention relates to an improved method of producing strengthened Fourdrinier wire, bearings, corrosion-resistant alloys, high-strength electrical conductor alloys and higher strength copper base alloys per se by adding molybdenum-coated molybdenum disulfide, in fine particle size to copper base alloys. And in particular the incorporated fine particles impart a builtin lubrication and thus a lower coefficient of friction to Fourdrinier wire and bearings.

It is an object of this invention to help maintain a fine grain size in copper alloys resulting in improved strength and toughness.

It is a further object of this invention to provide wires for electrical conduction with higher strength than standard copper-tin alloys currently used in industry, with a comparable electrical conductivity.

Another object of this invention is to improve the modulus of elasticity of a copper base alloy over that of standard alloys. More specifically this new strengthening method raises the modulus of elasticity to the range of 16.45X to x10? pounds per square inch as opposed to 16x10 for standard phosphor bronze (this value taken from the Metals Handbook). In this respect, the modulus of elasticity of the strengthened alloy equals or surpasses that of beryllium copper, considered the best or strongest copper base alloy (l6l8.5Xd as per Metals Handbook).

A still further object of this invention is to provide a wire which maintains a smoother surface in the presence of paper mill solutions than a regular phosphor-bronze wire.

A further object of this invention is to provide longer useful.

life for Fourdrinier wires, i.e., I ls-3 times that of regular phosphor-bronze wires when used in the presence of paper mill solutions.

Another object of this invention is to provide a Fourdrinier wire having a lower coefficient of friction without sacrificing yield strength.

Another object of this invention is to provide a copper base alloy having a higher tensile strength, a higher yield strength, a better electrical conductivity for a given yield strength, a lower coefficient of friction, a slower grain growth with annealing and some curved twin boundaries in some of the resulting alloy grains.

DRAWINGS P16. 1 is a graph of comparative grain sizes vs. temperature. FIG. 2 is a graph of comparative harness losses.

LII

PREFERRED EMBODIMENT The improved properties provided by this invention are ob tained by adding molybdenum-coated particles of molybdenum disulfide to a copper-tin melt. The particles are formed from molybdenum disulfide powder (250-500 mesh) which is deposited in a muffle of high nickel content and placed in a furnace for heating. The heating takes place in' a reducing atmosphere (H NH; or mixtures thereof) and the process requires approximately 2 hours at a temperature of approximately l,900 F. The result is an encompassing shell of molybdenum around each particle of the molybdenum disulphide. The process for producing the powder is set out in greater detail in US. Pat. No. 2,790,714.

A melt of copper and'tin is provided in any conventional manner and the coated particles in the proper percentage may be added to the ladle or fed into the pouring stream as the melt is dispensed from the ladle.

The key to the improved properties of the resulting alloy is the incorporated molybdenum disulfide. However, molybdenum disulfide per se cannot be directly incorporated into the melt to any significant extent. The coating of molybdenum is provided on the particle to facilitate incorporation. Bare molybdenum disulfide powder readily oxidizes to molybdic oxide and also tends to decompose to metallic molybdenum and sulfur at the usual pouring temperature of the melt, thus, the need for the coating.

In a tin-copper alloy, the atoms of tin may fit into the matrix of the face centered cubic copper crystal in the well-known al loying matrix structure. Also, pure molybdenum metal will alloy with pure tin. However, the exact mechanism by which the coated molybdenum disulfide combines with the coppertin alloy is not known with certainty, but it is believed that the molybdenum atoms and/or the molybdenum of the molybdenum disulfide molecules tend to alloy into the lattice structure of the tin, which structure is integrated with the face-centered cubic copper lattice as the melt freezes. That is, the tin alloys with the copper and because of the tin-molybdenum al.- loying relationship, some of the molybdenum atoms are carried into the face-centered cubic copper matrix. The result is believed to be a face-centered cubic copper-tin matrix with some molybdenum atoms lying in close proximity to, but not exactly at the 11 1 plane of the lattice.The mode may be sub.- stitutional or interstitial but atleast there is crowding" and distortion in the matrix and an absence of conclusive proof as to whether the positioning of the molybdenum atoms operate interstitially or substitutionally to strengthen the slip planes. The 111 plane is the expected slip" plane for this alloy and for some reason the proximity of the molybdenum atom to the lll plane provides a slippage barrier" which results in increased tensile and yield strength.

It is well known that molybdenum disulfide has excellent lubricating characteristics when incorporated in an alloy, and molybdic oxide does not have these properties; thus, the lubricating value of the molybdenum disulfide additive is vitiated when added to the melt without the coating. The molybdenum metal surrounding the molybdenum disulfide particle comprises from about 10 to 20 percent of the total weight of the particle. It is believed that molybdenum disulfide and/or molybdenum metal unite with the tin, and the tin in turn goes into solid solution with the copper, but with additional crowding due to the combination of the molybdenum disulfide and molybdenum with the tin. It must be stated that mere extra crowding in an alloy is not necessarily new and novel but the observed physical properties of this particular alloy recipe do appear to be new. The following properties have been observed and are believed to be new and unexpected results of the new alloy:

a. improved tensile strength b. improved yieldstrength c. improved modulus of elasticity d. harder wires with similar compositions where the M08 is incorporated e. microstructural evidence of annealing twin boundaries being curved in some grains f. Fourdrinier wires in paper mill solutions had longer useful life and the wires corroded smooth rather than pitted or rough.

Various tests were conducted on the alloy of this invention with the following data obtained:

Modulus of Elasticity (approximately 92.78% Cu, 6.97% Sn and 0.25% M052);

Sample I (Torsion Test) 16.4!00 p.s.i.

Sample 2 (Torllon Test) 17.00Xl p.s.i.

Sample 3 (Torlion Test) 17.35X10 p.s.i.

Sample 4 (Torsion Test) 17.7 X10" p.s.i.

Sample 5 Tension Test) 19.3 X p.s.i.

Sample 6 (Tension Test) 2O.00 l0 p.s.i.

Phosphor Bronze (Book Value-92% Cu, 8% Sn) 16.0 X10" p.s.i.

0.5% Offset Yield Strength (same percentage components in samples):

Sample 7 S l ,000 p.s.i.

Sample 8 52,200 p.s.i.

Phosphor Bronze 24,000 p.s.i.

Copper 10,500 p.s.i.

Tensile Strength (same percentage in samples):

Sample 9 73,000 p.s.i. Sample 10 74,000 p.s.i. Phosphor Bronze 63-61000 p.s.i. Copper 32,000 p.s.i.

Coefficient of Friction (kinetic):

Tests A-F ills-0.19%

Phosphor Bronze (Book Value) 0.25% Useful life of woven Fourdrinier wire (wear to one-half of original warp diameter in paper mill solution):

Sample 41 (same composition) 250 hrs. Phosphor Bronze (92% Cu, 8% Sn) l60 hrs.

Within the knowledge of the inventor there are no other tertiary or quaternary alloy systems which operate in the same manner as the copper-tin-molybdenum and/or molybdenum disulfide system described, that is, where two of the components form solid solutions and the third and/or fourth is not miscible with one of the other first two components.

Concerning the strengthened wires useful for electrical conductivity (electrical transmission), a range of 0.25-1 .0% tin is used conventionally. Also, a small amount of cadmium is sometimes used to strengthen the alloy. A problem of toxicity exists with wire production with respect to the cadmium and it is desirable to eliminate it. No such problem exists with molybdenum disulfide. The essence of the improvement in this field is that the cadmium may be eliminated and a smaller percentage of tin may be used for a given yield strength. Reducing the amount of tin increases the electrical conductivity. The result is an increased electrical conductivity for an equivalent yield strength.

The reduced coefficient of friction indicated by the tests tabulated above give bearings of the alloy of this invention a much longer useful life.

The curved twinning planes were observed in some alloy grains by employing the conventional etching and polishing technique and the curved planes" are probably part of the reason for the increased tensile strength. Obviously, a linear force impinging on a curved surface transmits a lower net linear force than an equivalent force impinging on a flat surface. Therefore, a greater force is required to cause slippage. It is hypothesized that the fact that the molybdenum atoms fall in proximity" to the l l l slippage plane of the lattice either through a substitutional or interstitial mechanism, but not exactly in the plane, contributes to the curved twin boundaries. However, the exact mode is not known with certainty.

Tests have indicated that for various uses the tin content may range from 0.25-1 1% and the molybdenum disulfide content may range from 0.1-0.5%. The particular percentages will be dictated by the intended use of the alloy; for example, an alloy of 6-7.5% Sn, 93.9-92% Cu and 0.l-0.5% M08 is preferred for the manufacture of Fourdrinier wires; a similar molybdenum disulfide percentage with less than 1% tin and 99.75-98.5% copper is preferred for wires for electrical transmission and; 0.l-0.5% M08 up to 11% Sn with the balance Cu is preferred for bearings (the lead usually added to bearings being eliminated).

FIG. 1 is a graph of compiled test data on the grain growth of various materials. As can be observed, a much slower grain growth rate is obtained for the alloy of this invention. The slower grain growth rate results in a consistently finer grain in the alloy. As is know, the fine-grain characteristically gives a greater strength, a higher fatigue resistance and a greater resistance to wear and deterioration under conditions of frictional heating. Fourdrinier wires, for example, arerepeatedly exposed to flash temperatures of 350-450" F. in running over some fixed wearing surfaces.

The loss of hardness data compiled and recorded on the graph in FIG. 2 clearly show the superior hardness retention of the alloy of this invention compared to currently used materials. The hardness data results from tests conducted according to Indentation Hardness Testing by Vincent E. Lysaght,

Chapter 15 beginning on page 188, which was published in 1949 by Rinhold Publishing Co.

Various modifications will readily occur to those having ordinary skill in the art. In this regard, it is not intended that the language used to describe the preferred embodiment be limiting on the invention. Rather it is desired that the invention be limited only by the appended claims.

I claim:

1. A copper base alloy including about (3-7.5 percent tin and about 0.10.5 percent molybdenum disulfide, said copper and tin being substantially completely in solid solution.

2. A copper base alloy including about 025-1 1 percent tin and about 0. l-0.5 percent molybdenum disulfide, said copper and tin being substantially completely in solid solution.

3. A copper base alloy including not greater than about 1 percent tin and about 0.l-0.5 percent molybdenum disulfide, said copper and tin being substantially completely in solid solution.

4. A copper base alloy including not greater than about 1 1 percent tin and about 0. l0.5 percent molybdenum disulfide, said copper and tin being substantially completely in solid solution.

5. An alloy for use as an electrical conductor including about 0.25-1 percent tin, 0. l-0.5 percent molybdenum disulfide and 99.6598.5 percent copper, said copper and tin being substantially completely in solid solution.

6. A copper base alloy which corrodes smooth in paper mill solutions including about 0.25-11 percent tin and about 0.l-0.5 percent molybdenum disulfide, said copper and tin being substantially completely in solid solution.

7. A bearing comprising about 0.1-0.5 percent M08 not substantially greater than about 1 1 percent Sn and the balance Cu, said copper and tin being substantially completely in solid solution.

8. A copper base alloy produced from a substantially complete melt of the constituents including about 6-7.5 percent tin and about 0. l-0.5 percent molybdenum disulfide.

9. A copper base alloy produced from a substantially complete melt of the constituents including about 0.25-11 percent tin and about 0. l0.5 percent molybdenum disulfide.

10. A copper base alloy produced from a substantially complete melt of the constituents including not greater than about 1 percent tin and about 01-05 percent molybdenum disulfide.

11. A copper base alloy produced from a substantially complete melt of the constituents including not greater than about 11 percent tin and about 0.1-0.5 percent molybdenum disulfide. v

12. An alloy produced from a substantially complete melt of the constituents for use as an electrical conductor including about 0.25-1 percent tin, 01-05 percent molybdenum disulfide and 99.65-98.5 percent copper.

13. A copper base alloy produced from a substantially 14. A bearing produced from a substantially complete melt complete melt of the constituents which corrodes smooth in of the constituents comprising about 0.1-0.5 percent M08 paper mill solutions including about 0.25-11 percent tin and not substantially greater than about 11 percent Sn and the about 1-0.5 percent molybdenum disulfide p 7 balance Cu. 

2. A copper base alloy including about 0.25-11 percent tin and about 0.1-0.5 percent molybdenum disulfide, said copper and tin being substantially completely in solid solution.
 3. A copper base alloy including not greater than about 1 percent tin and about 0.1-0.5 percent molybdenum disulfide, said copper and tin being substantially completely in solid solution.
 4. A copper base alloy including not greater than about 11 percent tin and about 0.1-0.5 percent molybdenum disulfide, said copper and tin being substantially completEly in solid solution.
 5. An alloy for use as an electrical conductor including about 0.25-1 percent tin, 0.1-0.5 percent molybdenum disulfide and 99.65-98.5 percent copper, said copper and tin being substantially completely in solid solution.
 6. A copper base alloy which corrodes smooth in paper mill solutions including about 0.25-11 percent tin and about 0.1-0.5 percent molybdenum disulfide, said copper and tin being substantially completely in solid solution.
 7. A bearing comprising about 0.1-0.5 percent MoS2, not substantially greater than about 11 percent Sn and the balance Cu, said copper and tin being substantially completely in solid solution.
 8. A copper base alloy produced from a substantially complete melt of the constituents including about 6-7.5 percent tin and about 0.1-0.5 percent molybdenum disulfide.
 9. A copper base alloy produced from a substantially complete melt of the constituents including about 0.25-11 percent tin and about 0.1-0.5 percent molybdenum disulfide.
 10. A copper base alloy produced from a substantially complete melt of the constituents including not greater than about 1 percent tin and about 0.1-0.5 percent molybdenum disulfide.
 11. A copper base alloy produced from a substantially complete melt of the constituents including not greater than about 11 percent tin and about 0.1-0.5 percent molybdenum disulfide.
 12. An alloy produced from a substantially complete melt of the constituents for use as an electrical conductor including about 0.25-1 percent tin, 0.1-0.5 percent molybdenum disulfide and 99.65-98.5 percent copper.
 13. A copper base alloy produced from a substantially complete melt of the constituents which corrodes smooth in paper mill solutions including about 0.25-11 percent tin and about 0.1-0.5 percent molybdenum disulfide
 14. A bearing produced from a substantially complete melt of the constituents comprising about 0.1-0.5 percent MoS2, not substantially greater than about 11 percent Sn and the balance Cu. 